Traditionally, U-shaped or “gooseneck” traps have been used in the plumbing industry to prevent backflow of harmful or undesirable sewer or pipe gasses into buildings while permitting drainage of unwanted liquid from floors and other generally horizontal surfaces. Such traps operate by leaving a small quantity of fluid within the lower portion of a U-shaped trap section to act as a gas barrier. In many applications, however, particularly where access is difficult or where drainage is infrequent, gooseneck traps are not optimal. Fluid in gooseneck trap may evaporate from the trap, permitting free flow of obnoxious gasses through the drain, insects may breed in the fluid, or in some instances the fluids may harden so as to actually block or restrict flow through the drain. Such conventional drains are also relatively difficult and expensive to install.
Drains with check valves have been developed to overcome some of the shortcomings of the gooseneck traps. See, For example, U.S. Pat. No. 6,273,124 to Huber et al and U.S. Pat. No. 6,719,004 to Huber et al. Such drains are effective in facilitating draining operations and in trapping drain-pipe gasses and preventing backflow. However, check valve type drains with further improvement in their effectiveness, manufacturability, reliability, and ease of use are desirable. Check valves with the ability to resist back pressure from the drain in order to test for leakage or other anomalies would be desirable.